1. Field of Invention
The present invention relates to a variable reflectance mirror that changes its reflectance by developing and fading color of a color layer provided on the side of a light-reflecting layer thereof electrically, or by hydrogen-containing gas or the like.
2. Description of the Related Art
Variable reflectance mirrors, that change their reflectance by electrically coloring color layers formed on surfaces of light-reflecting layers, has been conventionally known (e.g., Japanese Utility Model Application Publication (JP-Y) No. 62-2587).
In the variable reflectance mirror disclosed in JP-Y No. 62-2587, thin layers consisting of a transparent electrode, hydroxide iridium (Ir(OH)3) layer, tantalum pentoxide (Ta2O5) layer, tungsten trioxide (WO3) layer, and an aluminum (Al) electrode, are formed (laminated) in this order on a rear surface of a glass substrate by means of, for example, a vacuum deposition. In the variable reflectance mirror, when a voltage is applied between the transparent electrode and the aluminum electrode, the iridium hydroxide layer and the tungsten trioxide layer undergo a coloring reaction, thereby resulting in change of a reflectance of the mirror.
However, in some cases, a variable reflectance mirror having the above-described configuration once colored can not be restored to the decolored condition, if thickness and qualities of respective thin layers described above are not well balanced. Further, because fluctuation in thickness of the layers significantly affects properties of the mirror, such mirrors require difficult manufacturing conditions and thus increase in production cost due to use of vacuum deposition or the like for production of the multilayer films.
In view of overcoming these problems, a variable reflectance mirror with a simpler configuration having only two layers on a rear surface of a glass substrate has been proposed.
As shown in FIG. 6, in the variable reflectance mirror 100, a tungsten trioxide color layer 104 that develops color by binding to hydrogen or lithium is formed on a rear surface of a glass substrate 102, and a light-reflecting rhodium layer 106 that allows permeation of hydrogen or lithium is formed on a side of the color layer 104 that is opposite to side on which the glass substrate 102 is formed. In addition, the variable reflectance mirror 100 has a supplying device (not shown) that supplies hydrogen or lithium to the color layer 104.
In the variable reflectance mirror 100, when hydrogen or lithium is supplied to the color layer 104 by the supplying device, the color layer 104 develops color by binding to hydrogen or lithium. As a result, the light that enters from the surface of the glass substrate 102 (top surface in FIG. 6) into the glass substrate 102 and is reflected by the light-reflecting layer 106 becomes reduced in intensity while passing through the colored color layer 104, resulting in decrease in reflectance.
The variable reflectance mirror 100 having the configuration above should have theoretically a high reflectance of 63% when the color layer 104 has been decolored, if the color layer 104 is made of tungsten trioxide and the light-reflecting layer 106 of rhodium as described above.
However, in reality when the tungsten trioxide color layer 104 is formed, for example, by vacuum deposition, sol-gel, or other method, the surface 108 becomes uneven and part of the rhodium light-reflecting layer 106 becomes overlapping with the color layer in the irregularities as shown in FIG. 6. It has been theoretically confirmed that the presence of such irregularities at the interface between the two layers makes the interface indistinct and thus reduces the reflectance of the mirror when the color layer 104 has been decolored. In addition, an increase in the depth (h) of interface irregularities leads to drastic decrease in reflectance.
For example, when a tungsten trioxide color layer 104 having a thickness of 500 nm is formed by vacuum deposition, the depth h of the irregularities becomes 10 to 20 nm; and in such a case, it has been confirmed that the reflectance decreases by tens of % to 50% or less as shown in FIG. 7.